1. Field Of The Invention
The present invention relates generally to television systems, and more particularly to anamorphic television systems.
2. Related Art
Television systems are designed to conform to standards defining parameters such as the number of scan lines per frame, the scanning line rate, and the frame rate for generating the displayed image. These standards also specify the format aspect ratio of the displayed image. Format aspect ratio is defined as the ratio of image width to image height.
Typical standards issued by the United States Electronic Industries Association include RS-170 for systems with 525 total scan lines per frame and RS-343-A for high resolution systems with 675, 729, 875, 945 and 1023 scan lines per frame. These standards are fully described in Electronic Industries Association EIA standard RS-170, "Electrical Performance Standards--Monochrome Television Studio Facilities," revision TR-135, and Electronic Industries Associations EIA standard RS-343-A, "Electrical Performance Standards for High Resolution Monochrome Closed Circuit Television Camera." These references are hereby incorporated in their entirety into this disclosure. These standards both specify a format aspect ratio of 4:3 which has been a universally accepted aspect ratio for broadcast and cable TV as well as most industrial and military television system applications. In addition, RS-343-A A specifies 946 active scan line of video information for each frame of a 1023 line system and 809 active scan lines per frame for an 875 line system.
Some conventional television systems use electron-beam scanning of the camera tube for image pickup and of the cathode ray tube for image display. Other conventional systems use solid-state image sensors such as charge-coupled device (CCD) image sensors for image pickup.
The display device of conventional television systems can be a cathode ray tube with electron-beam scanning or a solid-state display. Solid-state displays typically consist of a matrix of light-emitting or light-controlling elements with support electronics configured to provide displayed images of television video signals.
Systems using electron-beam scanning techniques can be easily modified to conform to different scan rates, frame rates, and format aspect ratios as specified by the various standards. With electron-beam scanning, these changes typically only require adjusting the frequencies and/or amplitudes of the scan signal wave forms.
Solid-state image sensors, however, afford only limited flexibility to conform to multiple standards. These sensors are designed and fabricated with a fixed number of element rows. The number of rows is chosen to correspond to the number of scan lines per frame specified by the chosen standard. Also fixed is the width of each element row. This dimension is chosen to provide the specified format aspect ratio. The number of picture elements (pixels) per element row determines the horizontal resolution of the image sensor. A greater number of pixels per row results in improved horizontal resolution.
Since the number of rows, the width of the rows, and the number of pixels per row is fixed in solid-state image sensors, conventional television systems implementing such devices have limited flexibility. Two examples provided below illustrate the limitations of conventional solid-state image sensor television systems.
The first example illustrates why a conventional television system designed to operate at 972 active scan lines per frame with a format aspect ratio of 4:3 and 1134 pixels per scan line, will operate at reduced resolution if implemented in an application requiring only 809 active scan lines per frame. In conventional systems an opticla image is formed or relayed using a conventional lens or conventional fiber optic taper so that the useful portion of the image impinges on only 809 of the 972 sensor rows. The reduced image size is 809/972, or 83%, of the original image size. Since the image is reduced by 83% along both axes, only 83%, or 943 of the 1134 pixels along each row are used. The result is a television system which operates at reduced horizontal resolution.
The second example illustrates why a conventional television system designed to operate at a given format aspect ratio will have limited flexibility to conform to standards specifying other format aspect ratios. Consider the same conventional system as in the first example having 972 active scan lines per frame and a format aspect ratio of 4:3. If this system is used to operate with a format aspect ratio of 16:9, a reduction in the number of scan lines and a reduction in resolution along the vertical axis results. The 16:9 image has a width of 16 units and a height of 9 units. The 4:3 sensor, which can also be expressed as a 16:12 sensor {4.times.(4:3)}, has a width of 16 units and a height of 12 units. When a 16:9 image impinges upon a 16:12 sensor, only 9 twelfths, or 75%, of the active scan lines are utilized. This results in a reduction of vertical resolution. Also, the loss of scan lines can result in failure to conform to a given scan-line standard.
In summary, conventional television systems using solid-state image sensors cannot effectively be used in multiple applications specifying various standards. Where limited quantities are required, the cost of redesign and fabrication of a unique solid-state image sensor for each application of the conventional television system becomes a significant factor in television system cost. Also, due to size, power, weight, and thermal constraints, conventional systems using electron-beam-scanned image sensors may not provide a viable alternative to solid-state image sensor systems.